Changing enum values

Question

Why does the following code throw an exception?

I need to persist enum values, and I am guessing the best practice for persisting the enum values in database is to store them as lower case string literals and hence this effort.

public enum Type {

SWIPE_BUTTON("swipe_button"), DROP_DOWN("drop_down"), RADIO_BUTTON("radio_button"), CHECK_BOX("check_box");

private final String label;

private Type (String label) {
    this.label = label;
}

public String getValue() {
    return label;
}

@Override
public String toString() {
    return getValue();
}

public static Type getEnum (String value) {

    for (Type type : values())
        if (type.getValue().equals(value)) return type;

    throw new IllegalArgumentException("invalid value for type");
}

public static void main (String[] args) {

    System.out.println(Type.valueOf("swipe_button"));
}
}

I found this approach here.

UPDATE

Looks like I was essentially trying to override the valueOf method, and the answer is it is not possible to do so. I was trying to override this method so that when my JPA database mapper tries to auto populate the entity object from database I can convert the lower-cased string literals (in database) to their uppercased enum constants. I shall retort to persisting the enums with their names itself (i.e. uppercased).

Because there is no Type instance named `"swipe_button"`. There is one named `SWIPE_BUTTON` though. — JB Nizet, Aug 28 '16 at 13:06
Why bother defining `getEnum` if you're not going to call it? — Andy Turner, Aug 28 '16 at 13:09
Another hint: Type is a really really bad name for an enum. Everything is a **type**. Call it "SelectionType" or whatever. — GhostCat, Aug 28 '16 at 13:11
"I am guessing the best practice" Why would it matter whether they are upper or lowercase? — Andy Turner, Aug 28 '16 at 13:11
Ok, I think I will just persist them uppercased, i.e., with their names. — Rocky Inde, Aug 28 '16 at 13:14

ΦXocę 웃 Пepeúpa ツ · Accepted Answer · 2016-08-28T13:16:36.157

2

I need to persist enum values, and I am guessing the

no need for that complex approach...

instead do something like

public enum Type {

SWIPE_BUTTON, DROP_DOWN, RADIO_BUTTON, CHECK_BOX;
}

and get the name of the constants in the enumerator (that is what you need at the end...)

save the Type.name() instead...

edited Aug 28 '16 at 13:16

answered Aug 28 '16 at 13:10

ΦXocę 웃 Пepeúpa ツ

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would that be lowercase or still capitalized in the database? – Rocky Inde Aug 28 '16 at 13:12
it would be the same as they are defined in the enum... name is a String so if lowercase is required you can do ***Type.name().toLowerCase()*** – ΦXocę 웃 Пepeúpa ツ Aug 28 '16 at 13:13
Another complexity is that my clients write to DB as lower cased and when fetching I am trying to auto populate the entity object using Spring's MongoDB mapper which uses the `Enum.valueOf` directly. – Rocky Inde Aug 28 '16 at 13:21
then when read it from DB use Enum.valueOf(stringRestored.toUpperCase()) – ΦXocę 웃 Пepeúpa ツ Aug 28 '16 at 13:24
The mapper library does that in it's code. Hence, I was trying to override this method which I guess is not possible. – Rocky Inde Aug 28 '16 at 13:29

score 1 · Answer 2 · answered Aug 28 '16 at 13:08

1

Enum.valueOf works with the name, it doesn't work with the string you assigned, so you should use Type.valueOf("SWIPE_BUTTON"), as the name is uppercase.

Likely you meant Type.getEnum("swipe_button").

answered Aug 28 '16 at 13:08

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GhostCat · Answer 3 · 2016-08-28T13:20:11.740

When you iterate the possible enum constants, like

for (Type t : values() ) {
  System.out.println("t name:" + t. name());

you will find that enums are built on their NAMES.

Keep in mind: building enums from strings has to work for all kinds of enums. Thus the whole mechanism is based on a fixed property of each enum constant - and that would be ... well, its name.

Thus: if you want to use that magic "valueOf()" method; then you have to follow the rules that this method and the magic behind it actually use.

Changing enum values

3 Answers3